Laser systems including fiber amplifiers are commonly used in many applications, including telecommunications applications and high power military and industrial fiber optic applications. Fiber amplifiers generally include optical fibers that passively transmit optical power, fibers that experience or are designed to enhance performance of a laser through nonlinear optical processes such as Raman-shifting and Brillouin scattering, and/or optical fibers that are doped with a lasing ion embedded in the fiber material (i.e., gain fibers).
Although laser systems generate coherent output power in a manner that is intrinsically efficient, the quantum defect limit (i.e., the difference in the photon energy at which the process is pumped versus the energy of the radiated “lasing” photons), spontaneous radiation losses, miscellaneous optical absorption losses, and other non-productive processes lead to a thermal energy release that heats the fiber amplifier. Elevated temperatures in the fiber amplifier can degrade the efficiency of the laser system, lead to unacceptable optical distortions or, in the extreme, to failure of the fiber amplifiers or surrounding system materials and components.
One approach to controlling the temperature of gain fibers and fiber-amplifier systems is to wrap the gain fiber around a heat-sink device such as a mandrel. Conventional gain-fiber mandrels have a direct and continuous line contact between the surface of the mandrel (generally a metal surface) and one side of the fiber (generally a glass). This design causes the fiber to reach high temperatures due to poor thermal contact and results in a non-uniform temperature gradient in the fiber. The high temperatures and non-uniformity of temperature experienced by a gain-fiber that is cooled by a conventional gain-fiber mandrel causes the fiber to degrade, which, in turn, leads to a power drop of the fiber amplifier. As power to a fiber-amplifier system that is cooled with a conventional gain-fiber mandrel is turned on and off, the fiber also experiences stress fatigue due to the difference of the coefficient of thermal expansion between glass (the fiber) and metal (the surface of the mandrel). Fatigue stress also degrades the fiber and thus also leads to a power drop of the fiber amplifier.
U.S. Pat. No. 6,301,423 issued Oct. 9, 2001 to Grieg A. Olson, titled “METHOD FOR REDUCING STRAIN ON BRAGG GRATINGS,” (hereinafter, “Olson '423”) is incorporated herein by reference. Olson '423 describes a method for securing an optical fiber Bragg grating to a retaining element having a helical groove. In accordance with the method, an optical fiber Bragg grating is wrapped around the retaining element so that the optical fiber Bragg grating extends in and along the helical groove. Next, an excess length of the optical fiber Bragg grating is provided in the helical groove to substantially alleviate tension exerted upon the optical fiber Bragg grating. Finally, the first and second ends of the fiber Bragg grating are affixed to the retaining element.
U.S. Pat. No. 6,424,784 issued Jul. 23, 2002 to Grieg A. Olson, titled “GRATING COIL PACKAGE FOR REDUCED FIBER STRAIN,” (hereinafter, “Olson '784”) is incorporated herein by reference. Olson '784 describes a method for securing an optical fiber Bragg grating to a retaining element having a helical groove. In accordance with the method, an optical fiber Bragg grating is wrapped around the retaining element so that the optical fiber Bragg grating extends in and along the helical groove. Next, an excess length of the optical fiber Bragg grating is provided in the helical groove to substantially alleviate tension exerted upon the optical fiber Bragg grating. Finally, the first and second ends of the fiber Bragg grating are affixed to the retaining element.
U.S. Pat. No. 6,968,112 issued Nov. 22, 2005 to James M. Zamel et al., titled “COMPACT PACKAGING OF MULTIPLE FIBER LASERS,” (hereinafter, “Zamel et al.”) is incorporated herein by reference. Zamel et al. describe a compact fiber packaging system for fiber lasers that comprises a series of spools nested inside one another for efficient volume utilization. The spools comprise an inner spool nested inside at least one outer spool to form a module. Generally, the fiber lasers are wrapped around the inner spool, and then around successive outer spools as required to form the module. Furthermore, the modules may be stacked to form a fiber assembly. The compact fiber packaging system further comprises devices and methods for minimizing thermal gradients between fibers and for removing waste heat from the system. Additionally, the available volume is further utilized by disposing equipment and materials for operation of the fibers inside a hollow center defined by the inner spool, between the nested spools, and adjacent the nested spools.
U.S. Pat. No. 7,044,768 issued May 16, 2006 to Donald E. Tilton et al., titled “LIQUID THERMAL MANAGEMENT SOCKET SYSTEM,” (hereinafter, “Tilton et al.”) is incorporated herein by reference. Tilton et al. describe a liquid thermal management socket system for thermally managing an electronic device in a socket. The liquid thermal management socket system includes a thermal management unit having a chamber for receiving one or more electronic devices, a plurality of first connectors within the thermal management unit for electrically coupling with the electronic device, and a plurality of second connectors electrically coupled to the first connectors, wherein the second connectors extend from the thermal management unit for electrically coupling within a socket unit on a board. The thermal management unit may have a cap member attachable to a base portion in a sealed manner. The chamber within the thermal management unit may thermally manage an electronic device within via spray cooling, liquid immersion or other liquid cooling method.
U.S. Pat. No. 7,400,812 issued Jul. 15, 2008 to Martin Seifert, titled “APPARATUS AND METHODS FOR ACCOMMODATING LOOPS OF OPTICAL FIBER,” (hereinafter, “Seifert”) is incorporated herein by reference. Seifert describes an optical apparatus for accommodating optical fiber, such as one or more loops of optical fiber. The optical apparatus can include a body comprising an inwardly facing surface adapted for receiving a plurality of loops of a length of optical fiber. The body can include at least a portion wherein the inwardly facing surface is continuous between two adjacent loops. Methods and apparatus are disclosed for disposing the optical fiber with an optical apparatus for accommodating the optical fiber.
U.S. Pat. No. 7,457,502 issued Nov. 25, 2008 to James Albert Davis, titled “SYSTEMS AND METHODS OF COOLING A FIBER AMPLIFIER WITH AN EMULSION OF PHASE CHANGE MATERIAL,” (hereinafter, “Davis”) is incorporated herein by reference. Davis describes a system for cooling a fiber amplifier includes a fiber amplifier assembly, which, in turn, includes a longitudinally-extending fiber amplifier, a jacket and a retaining structure. The jacket surrounds the fiber amplifier and extends at least partially longitudinally therealong. In this regard, the jacket surrounds the fiber amplifier such that the fiber amplifier assembly defines a passage between the jacket and the fiber amplifier for the circulation of coolant therethrough. To facilitate the circulation of coolant, the retaining structure is disposed within the passage defined by the fiber amplifier assembly for at least partially maintaining a spacing between the fiber amplifier and jacket. The retaining structure and coolant can both comprise an emulsion of phase change material.
U.S. Pat. No. 7,957,623 issued Jun. 7, 2011 to Tullio Panarello et al., titled “DEFORMABLE THERMAL PADS FOR OPTICAL FIBERS,” (hereinafter, “Panarello et al.”) is incorporated herein by reference. Panarello et al. describe a system for fiber optic packaging includes a first substrate and a first deformable pad coupled to the first substrate. The first deformable pad is characterized by a thermal conductivity greater than 1 W/mK. The system also includes a fiber coil having at least a portion embedded in the first deformable pad to provide physical contact between the at least a portion of the fiber coil and the first deformable pad. The system further includes a second substrate coupled to the fiber coil and at least a portion of the first deformable pad.
U.S. Patent Application Publication 2010/0247055 (which issued as U.S. Pat. No. 8,340,482 on Dec. 25, 2012) to Yoshihiro Arashitani et al., titled “OPTICAL FIBER HOLDING APPARATUS,” (hereinafter, “Arashitani et al.”) is incorporated herein by reference. Arashitani et al. describe an optical fiber holding apparatus characterized in that the same comprises a surface in order to hold an optical fiber which is to be a state of which is rolled up so as not to overlap with each other, wherein at least the surface is formed of a thermo conductive molding body which has a thermal conductivity to be higher than or equal to 0.5 W/mK, and which has an Asker C hardness to be between twenty and fifty. Or, the same comprises a peripheral surface in order to roll up and hold an optical fiber, wherein at least the peripheral surface is formed of a thermo conductive molding body which has the thermal conductivity to be higher than or equal to 0.5 W/mK, and which has the Asker C hardness to be between twenty and fifty. Moreover, it is desirable for the thermo conductive molding body to have a compressive strength of which a peak value is between ten and thirty N/cm.sup.2 and a stabilized value is between three and ten N/cm.sup.2. Furthermore, it is desirable for the thermo conductive molding body to have the thermal conductivity to be higher than or equal to 1.0 W/mK and to have the Asker C hardness to be between twenty-five and forty.
U.S. Patent Application Publication 2012/0085518 (which issued as U.S. Pat. No. 8,467,426 on Jun. 18, 2013) to Joseph Ichkahn et al., titled “METHOD AND APPARATUS FOR COOLING A FIBER LASER OR AMPLIFIER,” (hereinafter, “Ichkahn et al.”) is incorporated herein by reference. Ichkahn et al. describe a system and method for cooling an optical fiber includes a flexible heat sink member, a heat pipe evaporator, and a thermal storage medium. The flexible heat sink member is in thermal contact with the optical fiber. The heat pipe evaporator is configured to dissipate heat from the optical fiber. The thermal storage medium is in thermal contact with the flexible heat sink member and the heat pipe evaporator. The flexible heat sink member is configured to compensate for any mismatch in coefficient of thermal expansion between material of the optical fiber and material of the flexible heat sink member so as to provide radial compliance and to maintain direct thermal contact between the optical fiber and the flexible heat sink member.
There remains a need for an improved method and system for packaging and cooling gain-fiber systems and fiber-amplifier systems.